Measuring the power of an electrical circuit is a vital goal in many different electrical applications. Electric power is typically defined as a rate at which electric energy is transferred by an electric circuit. When an electric charge moves from a high voltage level to a low voltage level through a potential difference, electric energy is transferred and power is consumed. In many appliances, the power is converted into other forms, like light and heat in a light bulb, or kinetic energy in an electric motor. Electric power is typically calculated by multiplying the voltage by the current.
There are three different types of power to be measured in a circuit that contains both resistive and reactive components. Active power is a measure of the power that is dissipated by the resistive components of a circuit. The reactive components of an electric circuit do not actually dissipate any power, but they do give the impression of power dissipation in the form of reactive power. The combination of reactive power and active power is called apparent power, and it is the product of a circuit's voltage and current. The three types of power may relate to each other in a trigonometric way represented by a right triangle with active power and reactive power on the smaller sides and apparent power on the hypotenuse.
Measuring active power in a circuit is desirable due to the fact that active power represents the actual power dissipated. Active power represents the capacity of the circuit to perform work in a period of time. In using a circuit to perform work, knowing the active power of the circuit is valuable for many reasons, including being able to predict behavior of the circuit and control the circuit accurately.
The process of measuring active power in a circuit with both resistive and reactive components can be challenging. When the circuit is powered by an alternating current power source, the presence of reactive components causes the cycle of the current to be out of phase with the cycle of the voltage. Normally, to provide a measurement of active power, there are three required measurements: the line voltage, the load current, and the load voltage. This can be difficult to do, based on the difference in phase between the load voltage and load current. Measuring the load voltage generally requires an increase in the expense and complexity of the electrical circuit. A system for measuring active power that does not require measuring the load voltage would significantly simplify the process of measuring active power, and provide an advantage over conventional systems and methods of power measurement.
Embodiments of the invention provide such a system for measuring active power that does not require measuring the load voltage. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.